1. Field of the Invention
The present invention relates to both thermal mass transfer processes and thermal dye transfer imaging. In particular the present invention relates to the use of a first thermal mass transfer coating on a substrate which may be mass transferred to essentially any receptor surface to provide an image-wise distributed background layer on the receptor surface having desirable dye receptivity to a subsequently thermally transferred dye. Non-imaged areas still retain the touch and appearance of the original, uncoated receptor surface. A computer program integrates color separation information into data to drive a thermal printer to deposit the thermal mass transfer coating onto substantially only those areas where the subsequent colors are to be deposited.
2. Background of the Invention
Thermal mass transfer and thermal dye transfer processes are technologies that bear some superficial similarities but which are distinct within the technical art. Both processes use a donor sheet and a receptor sheet. The thermal mass transfer donor sheet normally comprises a carrier layer with at least a thermally transferable colorant (a dye or preferably a pigment) in a heat softenable binder. The thermal dye transfer donor sheet comprises a carrier layer with at least a dye layer on the donor surface. The dye layer may consist of only dye or dye in a binder (the binder not transferring when the dye is thermally transferred). Both transfer sheets are used with the donor surface in intimate contact with a receptor material, and the donor sheet is heated in an imagewise manner (e.g., by thermal printheads, irradiation as by a laser or high intensity radiation transmitted through a mask or stencil) to transfer the image forming material. In the thermal mass transfer system, the donor layer is softened by the imagewise heating (and sometimes a receptor layer on the receptor sheet is contemporaneously softened), and the softened area is transferred to the receptor sheet. In thermal dye transfer, the dye is melted, sublimated, dissolved or vaporized to diffusively transfer to the receptor sheet and tends to be adsorbed and/or absorbed into the surface of the receptor element. The nature of the mechanism of adherence of the transferred image to the receptor sheet makes the nature of the surface of that receptor sheet important for each of the imaging processes. Surfaces which work well for receiving mass transfer images do not necessarily work well for thermal dye transfer. Furthermore, there are not many natural surfaces which can function as a high quality dye receptive surface.
U.S. Pat. No. 4,472,479 (Hayes et al.) describes a light barrier fluorescent ribbon for impact printing which comprises a carrier layer, and on one surface of the carrier layer a binder layer of wax or polymeric resin and fluorescent dye, and a barrier pigment within that layer or in a separate layer. The barrier pigment is a finely divided pigment of lustre-affecting reflective material (metal or metal appearing) which provides color toning of the fluorescent image.
Japanese Published patent application (Kokai) 1-258,990 discloses non-digital transfer donor sheets coated with heat meltable ink layer regions of 3 primary colors or 4 primary colors plus black and a region containing a fluorescent dye. Overprinting of the respective regions with fluorescent dye is disclosed. The dye image is formed by printing onto one sheet and then transferring the entire image.
Japanese Published patent application (Kokai) 63-281,890 discloses a recording material having a thermo-fusible ink layer containing a fluorescent compound and a thermo-fusible ink layer containing colorant and a thermo-fusible ink layer containing an extender with hiding power.
U.S. Pat. 3,647,503 describes a multicolored heat transfer sheet in which colored layers are sequentially coated on a substrate. That patent is directed at multicolored transfer imaging and requires good porosity of the uppermost layer to provide good transfer of dye from lower layers.
There is a need in the art, particularly in the proofing industry, to be able to apply dye images to many different substrates without losing the clarity of the image and without having to use complex processes. U.S. Pat. Nos. 4,923,848 and 5,077,263 disclose thermal dye processes in which the dye is first transferred onto a temporary receptor having a thermally laminable, dye-receptive, strippable layer on the surface of the temporary receptor. The strippable layer is transferred, along with the dye image to a final receptor surface. This process requires at least two imaging steps and two different types of imaging apparatus (the thermal dye imager and the laminator). There could be a polymer coating on top of the whole receptor substrate changing the substrate's appearance in the background areas.
U.S. Pat. No. 5,116,148 describes a thermal transfer sheet and a process of using it. The transfer sheet has dye transferable media and a precoating layer in separate areas. The precoating layer is laminated and transferred to a receptor sheet in advance of the dye transfer. There is no indication that the precoating layer is thermally mass transferable in an imagewise manner, and no imagewise transfer process is shown, although it is disclosed that the precoating layer can be formed only at the necessary parts on the recording sheet. Furthermore, in order to print properly according to their process, adhesion preventing layers have to be provided over the ink layer region and between the transferable dye receptive layer (precoating layer) and the donor substrate.
EPO Patent Application Serial No. 94.401594.0 overcomes deficiencies of the prior art in providing good quality thermal dye transfer images that are generated by thermal transfer onto thermal mass transfer deposited backgrounds. The clarity and variety of thermal dye transfer images produced by this method is improved by image-wise thermal mass transferring a clear (translucent to transparent, and uncolored) layer prior to dye transfer.